Electric Tankless Water Heater Features and Options
It’s always best to arm yourself with useful information when trying to choose an electric tankless water heater. Understanding common terms manufacturers use to describe their products and the features that make them unique can go a long way in helping you to make an informed decision. You will be better able to compare products in the same category, set your budget and ultimately find the right electric tankless water heater for your specific needs. Consider these crucial attributes when choosing an electric tankless water heater.
Flow Rate
GPM (Gallons per Minute)
Range: 4 – 8 (warm climate); 3 – 7 (cold climate)
Flow rate refers to a measure of the volume of water that is flowing through a water heater in a specific amount of time and depends on the speed of the water. The flow rate for an electric tankless water heater is measured in gallons per minute (GPM) based on a temperature rise.
Gallons per minute (GPM) is a measure of how much water the electric tankless water heater is able to heat every minute. In other words, how many steady GPM of hot water can the electric tankless water heater produce?
How to Determine Flow Rate
If an electric tankless water heater has a flow rate of 4 GPM, the unit will deliver 4 gallons of hot water per minute. Now, when it comes to the specific required flow rate of your household, you have to take into account the number of hot water fixtures that are used at once during peak usage. To arrive at the total GPM needed, sum up the GPM of each fixture/appliance.
If your household uses 2 showers at once, with each showerhead using 2.5 GPM, and a washing machine that uses 1.5 GPM, your peak hot water need is 6.5 GPM (2.5 +2.5+1.5 = 6.5).
The amount of water you use simultaneously and the local groundwater’s temperature can cause the flow rate to vary. In warm weather climate, flow rate ranges from 4 GPM to 8 GPM, but in cold climates, the flow rate can decrease to 3 GPM. A proportional level of energy (kW) is required to heat the water you need for your particular application.
It is important to keep in mind that the slower the flow of water through the electric tankless water heater, the larger the volume of water that can be heated.
«Note: Each model of electric water heater has a “flow rate,” measured in GPM, and when making your selection, it must be based on your desired outgoing hot water temperature. »
Typical GPM For Different Fixtures
| Fixture/Appliance |
Typical Flow Rates |
| Bathroom Faucet |
0.5 – 1.5 GPM |
| Shower |
1.0 – 2.0 GPM |
| Kitchen Faucet |
1.0 – 2.5 GPM |
| Dishwasher |
1.0 – 2.5 GPM |
| Clothes Washer |
1.5 – 3.0 GPM |
| Bathtub |
4.0 – 5.0 GPM |
| Multi-Compartment Wash Sink |
2.5 – 3.0 GPM |
Temperature Rise
Temperature rise is the difference between the outgoing heated water delivered by the electric tankless water heater and the incoming ground water temperature.
How to Determine Temperature Rise
Keep in mind these three factors when calculating temperature rise:
- The volume of water the unit is required to heat, or the flow rate
- The temperature of the incoming ground entering the unit.
- The desired temperature of the outgoing hot water from the unit
For example, if you desire a shower delivering water up to 120°F and you live in Miami with groundwater at 69°F, then you need a 51°F temperature rise (120－69 = 51).
The fact is that you want your electric tankless water heater unit to provide a sufficient supply of hot water at the minimum comfortable temperature during peak periods. This is where the size of the unit is important to take into consideration. You want to avoid getting a unit that is oversized or undersized because it will likely result in unwanted issues, like increasing operating costs, failure to meet peak demand, as well as water loss and wasted energy. Selecting the proper size unit requires choosing a model based on the amount of hot water needed during peak demand in your household in order to afford comfort and efficiency.
«Note: It’s important to determine the climate where you live to establish the most reliable average groundwater temperature.»
Groundwater Temperature by Region in North America
Cold vs. Hot
When choosing an electric tankless water heater, it’s beneficial to consider groundwater temperature. What is the temperature of your incoming water? How hot or cold is it? The temperature of the incoming groundwater varies throughout North America and often fluctuates during different seasons. The temperature of your groundwater is determined by which part of the country you live in and the climate.
Consider the climate zones below when sizing an electric tankless water heater.
| Regions |
Average Groundwater Temperatures |
| Northern Zone |
Between 37°F and 51°F |
| Central Zone |
Between 52°F and 61°F |
| Southern Zone |
Between 62°F and 77°F |
Keep in mind that manufacturers calculate flow rates based on particular temperature rise requirements, and as such, it’s important to get the proper GPM for your specific temperature rise need. If you live in a cold region, a unit with a large water flow type is ideal, since the temperature and flow rate will frequently drop 2-3 GPM in these areas.
«Note: Start with the expected coldest groundwater temperature for your region when calculating temperature rise.»
Calculating the Size of an Electric Tankless Water Heater
Electric tankless water heaters are sized by their flow rate. Since electric tankless water heaters are rated by the maximum temperature rise at a given flow rate, to determine the right size heater for your specific needs, you establish the flow rate and the temperature rise needed for your application, whether using a single appliance or multiple fixtures. In so doing, you are simply making a determination regarding the maximum volume of hot water needed during peak demand. Once that is established, you can search for a model with a GPM matching your established peak demand.
A unit’s GPM delivery can be affected by the incoming water temperature in the instance where the same electric tankless water heater is used in two different locations with different climates.
For example, if the incoming water temperature in Miami is 70°F and 47°F in Las Vegas, the same model electric tankless water heater will not deliver matching GPM in both locations. The unit in Las Vegas will have to work nearly twice as hard to achieve the desired temperature rise than the one in Miami, and in the process, deliver a lower GPM of hot water. You will need a larger electric tankless water heater in colder climate than in a warmer region to serve the exact number and types of fixtures/appliances so you don’t end up overworking your unit trying to reach the desired temperature rise.
Manufacturers provide sizing charts, which communicate the GPM of hot water that the heater can deliver under ideal conditions. After you have calculated your flow rate and the required temperature rise, you can compare/match your numbers to the manufacturer’s sizing chart in order to determine the appropriate model that is best for your specific needs.
«Note: If you live in a generally cold region, select an electric tankless water heater with a higher water flow rate because the unit will have to raise its temperature exceedingly above the ground temperature to reach the desired output delivery rate.»
Energy Factor
Range: 0.96 – 0.99
Energy factor is a measure of the portion of electricity that is transferred to the hot water.
Energy efficiency is important when selecting tankless electric water heaters. With that said, energy factor is used to indicate the level of efficiency that a unit is packing. The energy factors of tankless electric water heaters generally range from 0.96 to 0.99. Since 2015, the Department of Energy has required that residential tankless electric water heaters have an Energy Factor between .98 and 1.0.
While electric tankless water heaters are known to be power consumers, you can achieve as much as 8.7% energy savings annually if you select the right one. A model with the best energy efficiency rating will convert more energy into heat at a faster rate, which amounts to the unit delivering hot water faster.
Installation
The sleek compact designs of many modern units allow for them to be placed in both traditional and nontraditional locations, such as crawl spaces. No venting is required, but the first thing to consider is that installing a new electric tankless water system in your home’s electric system will likely require an upgrade of the existing electric service. Depending on you application, you may need multiple electric tankless heaters to accommodate your minimum flow rate.
It requires roughly 147 watts of electricity to heat water with a flow rate of 1 GPM by 1 degree Fahrenheit, and as a result, electric tankless water heaters will pull a large amount of electric current to achieve the desired delivery rate. This means that in many cases, installations with an upgrade in electric service is necessary and could prove expensive. Installation costs also vary between brands and models and increase if the house needs rewiring to accommodate the system. Electric water heaters can cost anywhere from $250 to $1,300 on to install. A commercial facility could require substantial and costly upgrades upwards of several thousand dollars.
«Note: The higher the flow rate through the electric water heater, the “larger” the unit size and the costlier.»
Applications
Electric tankless water heaters are versatile in where they can be used. They can be used in and beyond spaces where the conventional tank water heater is used and are ideal for use in unique spaces. Here are some of the common electric tankless water heater applications for you to keep in mind.
Residential Applications
Point-of-use and whole-house electric tankless water heaters are the two basic options for residential settings.
Point-of-Use
A point-of-use application is one in which an electric tankless water heater supplies only a single fixture/appliance and is installed near the delivery point. Hot water is received almost instantaneously after the fixture/appliance is turned on. This unit delivers hot water to a specific location, limiting the wait time for the water to heat. Beyond isolated hot water needs, this application can be used with a whole house system for additional hot water needs, specifically settings with multiple hot water sources.
Point-of-use systems are great for use under the sink in the kitchen or in a supply room or closet. A homeowner with an existing water heater could benefit from this unit, which could provide hot water to parts of the home that are distant from the existing unit, reducing or eliminating heat losses through piping.
Whole-House Use
A whole-house electric tankless water heater refers to a single unit that is designed to serve an entire home where multiple fixtures/appliances are used. There is usually a central location and this unit is the primary source of hot water. The hot water must travel to the fixtures and not instantaneously arrive, and this creates a wait time for hot water output. This could lead to heat loss, especially if the pipes are uninsulated.
These units are designed to serve an entire house or apartment, and supports a large volume of hot water, creating the need for installation near the main electricity panel. This will allow for quicker flow of hot water and greater efficiency. When there is a pattern of regular water use in a home, for example, where several people are getting ready for work and multiple taps are used for hot water, whole house indoor units are more suited.
Commercial Use
Electric tankless water heaters are beneficial for a wide range of commercial water heating applications. Identifying certain crucial characteristics is important when choosing the best electric tankless water heater for your business, such a hot water demand, peak hours, number of fixtures/appliances, and even location.
Commercial units have to be appropriately sized in order to accommodate your specific business needs and hot water requirements. If your unit is too small, it will not produce enough hot water when you need it the most, especially during times of high demand. Some are designed to heat water only when needed while some units provide point-of-use benefits.
Businesses with small client bases could benefit more from cheaper, compact commercial units, while other businesses may have a need for much larger and sturdier units that can supply a steady flow of hot water. Commercial units are ideal for use in hair salons, laundromats, restaurants, and even hotels, where a large demand for hot water needs to be met.
Warranty
Options: 0 years to Lifetime
It’s important to have some level of protection against a faulty or defective electric tankless water heater after you have made a purchase. Whether there is a problem with the entire unit itself, or a specific part, the warranty will determine if you will be responsible for the replacement cost or if you will not need to pay out of pocket.
You should protect your investment, so make an effort to select an electric tankless water heater with a 5-year warranty at least.
Different brands and product lines offer different warranty lengths and coverage. Take a look at these examples:
- Ecosmart ECO 27, at 240 volts, 112.5 amps with Patented Self Modulating Technology: Limited lifetime warranty on electronics, exchangers and elements under normal use and service after proper installation. Warranty only covers the cost of the heater and not labor.
- Rheem RTE 18 Electric Tankless Water Heater, 5 GPM: 1-year parts warranty. 10 years heat exchange warranty. Warranties are only valid if the unit was installed by a licensed technician.
Electric Requirements
Prior to installing your electric tankless water heater, it is vital that your electrical system is compatible with the unit. The appropriate amperage, circuit breaker type, voltage, and wire size are needed so that the unit can function properly and to ensure safety. Here are some electrical requirements to consider when planning to purchase an electric tankless water heater.
Voltage: It’s crucial that your home’s electrical system can accommodate 110V to 277V, since many units fall within that category.
- Bosch Tronic 3000: Requires 120 volts
- Stiebel Eltron Tempra 29 Plus 2: Requires 240- or 208-volt electric service
Amperage: Most models and brands have particular requirements in amperage draw to ensure that the electrical system is ready to handle the electrical demands of the unit you would like to buy.
- Bosch Tronic 3000: Requires 120 amps
- Stiebel Eltron Tempra 29 Plus 2: Requires a minimum of 200 amp total service, with three separate double-pole 40-amp breakers and three separate runs of 8-gauge copper wiring
Circuit breaker: You must have a circuit or a number of circuits, depending on the unit’s requirement, to effectively support your electric tankless water heater. You may find that the unit you are interested in buying will require its own circuit or circuits as well.
- The ECO 36 requires 4 x 40 Amps DP
- The ECO 8 requires only 1 x 40 Amps DP
« Note: Keep in mind that the total electric service for many homes falls short in being able to support an electric tankless water heater’s voltage and amperage requirement. You may have to rework your entire electrical system.»
Technology
Technology has allowed for the development of “smart” electric tankless water heaters. Microprocessing technology is a popular technological feature that enables computer-controlled monitoring, where the unit keeps the output temperature steady even if the flow rate goes up or down. Digital display thermostat allows for the display of the unit’s water temperature setting so it can be adjusted to the desired water temperature.
Consider this scenario
If you desire a temperature of 85 degrees Fahrenheit, but the incoming water temperature is an ambient 55 degrees, the microprocessor in a unit can read the temperature and adjust it, adding 30 degrees of warming power to allow it to reach the preferred temperature.
Flow control is another technological feature that enhances efficiency in an electric tankless water heater. It works by automatically reducing the flow of water slightly, delivering less water, but at the hot water temperature desired.
Self-modulation is another technological feature that some electric tankless water heaters are equipped with, and it ensures that only the least amount of energy is used to heat water every time.
Stiebel Eltron and Takagi are known for equipping particular models of their electric tankless water heaters with this technology.
Maintenance and Lifespan
Electric tankless water heaters require a minimal amount of maintenance, usually involving routine cleanings of the inlet screen filter. Problems are simpler to diagnose and repair because these units lack components like complex fuel controls and heat exchangers. An electric tankless water heater lasts an average of 20 years, typically being less exposed to moisture that can cause water-based corrosion.
Do You Even Need a Tankless Electric Water Heater?
An efficient tankless electric water heater can cost over $100 on the cheaper end, while on the more expensive end, a unit can cost over $1400. Either way, you are making an investment when you purchase a tankless electric water heater. As such, you want to ensure that you really need one before you spend money unnecessarily.
Steady comfort: Electric tankless water heaters can provide a near-constant supply of hot water for all your hot water needs, for as long as you need it. With microprocessing technological features, your system will not overheat and produce scalding water, there will be less water loss, and you will save on energy costs.
Convenience: Tankless electric water heaters are compact in design and, as such, are space-saving units. They are ideal for residential use in homes and condos, as well as outdoor showers and sinks. Advanced technological features like digital display thermostat makes it easy to adjust temperature settings and allows for improved accuracy and user control.
Conservation: Most models of tankless electric water heaters are known to reduce household energy bills, affording 8.7% energy savings annually. These units can last up to 20 years, on average, reducing the amount of waste in landfills.
If you intend to buy one of these units, consider your hot water needs, the demands, the number of fixtures/appliances you need to supply, location, and the kind of application that you have in mind. In so doing, you will have a clearer view of the size unit that you need and whether you will potentially need an upgraded electrical system to accommodate it.
Quick Tips
Here are the most important things to keep in mind when choosing a tankless electric water heater for personal use*:
- GPM and temperature rise determines size.
- The higher the unit’s energy rating, the higher the unit’s flow rate.
- Know the amount of energy required to raise the temperature of incoming water.
- Decide on an application.
- Point-of-use application, a single unit for one fixture/appliance, or multiple point-of-use sources.
- Whole-house application, a single unit serving an entire home with multiple fixtures/ appliances.
- Voltage and amperage should be compatible with electrical system.
- Know your climate requirements.
- The cooler the incoming water temperature, the higher the GPM rating needed.
- A higher GPM is more ideal for cold climates.
- For a more user-adjustable and accurate temperature reading, consider one with technological features, such as flow control and self-modulation
* For commercial use, look for units with high GPM that can provide a steady supply of hot water.
